It is common practice in the manufacture of electrical instruments to provide multiple metering functions within a single meter housing. For example, a wide variety of meters are now available in which certain options are incorporated to enable a single meter indicating mechanism to measure voltage, current and ohms or electrical resistance. Although such multi-function meters enjoy wide commercial application, many users frequently wish to purchase only a meter having one or two such metering functions built into it. Typically, the reason given by purchasers for specifying such a limitation is their desire to avoid the expense of purchasing a metering function that is not needed for a given meter application.
Prior to the present invention, it was common manufacturing practice to build circuitry into multi-function meters to enable them to provide voltmeter, ammeter and ohmmeter readings by using appropriate combinations of electrode probe leads selectively plugged into engagement with a common terminal mounted in the meter housing and with one of the other terminals associated with the circuitry to be used for measuring the selected function. Thus, if a user elected to purchase a meter having a single or dual function, rather than the triple function often built into such meters, the meter could only be subsequently adapted to measure electrical resistance by changing the circuitry within it and by plugging a terminal hole in the meter casing. At best, such expedients are inefficient and frequently cause manufacturers to simply elect not to supply a standard, single-function meter.
Considering the desire of meter users to have both low meter purchasing costs and optimum flexibility in the number of meter functions that need be purchased in a given combination, and considering the usual desire of meter manufacturers to realize the cost economies of mass production of meters satisfying their customers' wants, it is desirable to provide an inexpensive, mass producible means for quickly and easily adapting a single function meter, such as a voltmeter, to measure other functions also, such as electrical resistance. It would also be desirable to provide such means in a package assembly that is separate from the conventional meter housing structure, so that users could purchase the two components in independent transactions, at their sole election. A further desirable advantage of such an arrangement is that it eliminates the prior art requirement of providing a relatively large number of terminal sockets in a multi-function meter housing to afford the diverse functions that can be afforded with the present invention utilizing a single, separate probe assembly that is capable of being plugged into a standard terminal board on a meter housing.
Accordingly, a major object of the present invention is to provide a meter probe assembly that is useful to expand the range of functions that can be afforded with a single electrical meter having fixed circuitry.
Another object of the invention is to provide a meter probe assembly that enables a voltmeter to be adapted for use as an ohmmeter without requiring modification of the circuits or terminals on the meter.
A further object of the invention is to provide an electrical meter an a separate meter probe assembly that are operable as independent units so that users can purchase and operate the units independently.
Still another object of the invention is to provide a meter probe assembly that can be efficiently manufactured with mass production techniques to overcome the problems noted above relative to the use of prior art multi-function meters.
Still other objects and advantages of the invention will become apparent to those skilled in the art from the description of it given below considered in combination with the accompanying drawings.